Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a hard, calcified substance which forms on the walls of a blood vessel.
Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty, and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient's body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guidewire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guidewire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.
Coronary by-pass, angioplasty, and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular by-pass surgery, angioplasty, and atherectomy impractical
When techniques which treat individual lesion are not practical a technique known as percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. PMR was inspired in part by observations that reptilian heart muscles are supplied with oxygen primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing within a heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenisis.
In addition to promoting increased blood flow, PMR may also improve the condition of a patient through denervation. Denervation is the elimination of nerve endings. Wounds created during PMR result in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue. In one embodiment in accordance with the present invention, a fluid under pressure is forced into the wound formed by PMR. This fluid may include saline, contrast media, a therapeutic agent, a caustic agent, or any combination of these. Means for detecting contact 706 may be used to verify that electrode 30 is in contact with myocardial tissue when the fluid is delivered. Injecting a fluid including a radiopaque contrast media creates a radiopaque marker of the treatment site. Injecting a fluid including a therapeutic agent into the wound may enhance the angiogenic response of the body. Forcing fluid under pressure into the wound may also create collateral damage within an area proximate the wound. This collateral damage may include the rupturing of blood vessels, capillaries, and sinuses within the myocardium. This collateral damage will increase the healing response by angiogenisis.
A number of methods have been used to create channels in the myocardium during percutaneous myocardial revascularization. Methods of cutting include the use of knife-like cutting tools and cutting with light from a LASER. Radio frequency energy may also be used to burn or ablate channels or craters into myocardial tissue.